open WCF svc file error in IIS

I am using VS2010 + C# + .Net 4.0 + IIS 7.5 + Windows 7. When I open a WCF svc f开发者_StackOverflowile in IIS 7.0, there is some error like this, any ideas what is wrong?

System.BadImageFormatException: Could not load file or assembly 'foo.test' or one of its dependencies.

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Probably the application pool is configured to target CLR 2.0. You need to change it to target .NET 4.0:

Also make sure .NET 4.0 is registered by running:

%WINDIR%\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -i